1. Field of the Invention
The invention relates to aerodynamics of and cooling of hot turbine airfoil and end wall surfaces in a region where the airfoil and end wall meet such as an intersection of turbine vane airfoils and bands between which they radially extend and such as turbine rotor blades and the bases from which they extend radially outwardly.
2. Description of Related Art
A typical gas turbine engine of the turbofan type generally includes a forward fan and a booster or low pressure compressor, a middle core engine, and a low pressure turbine which powers the fan and booster or low pressure compressor. The core engine includes a high pressure compressor, a combustor and a high pressure turbine in a serial flow relationship. The high pressure compressor and high pressure turbine of the core engine are connected by a high pressure shaft. High pressure air from the high pressure compressor is mixed with fuel in the combustor and ignited to form a very hot high energy gas flow. The gas flow passes through the high pressure turbine, rotatably driving it and the high pressure shaft which, in turn, rotatably drives the high pressure compressor.
The gas flow leaving the high pressure turbine is expanded through a second or low pressure turbine. The low pressure turbine rotatably drives the fan and booster compressor via a low pressure shaft. The low pressure shaft extends through the high pressure rotor. Most of the thrust produced is generated by the fan. Marine or industrial gas turbine engines have low pressure turbines which power generators, ship propellers, pumps and other devices while turboprops engines use low pressure turbines to power propellers usually through a gearbox.
The high and low pressure turbines have at least one turbine nozzle including at least one row of circumferentially spaced apart airfoils or vanes radially extending between radially inner and outer bands. The vanes are usually hollow having an outer wall that is cooled with cooling air from the compressor. Hot gases flowing over the cooled turbine vane outer wall produces flow and thermal boundary layers along hot outer surfaces of the vane outer wall and end wall hot surfaces of the inner and outer bands over which the hot gases pass. The high and low pressure turbines also have at least one row of turbine rotor blades including circumferentially spaced apart airfoils extending radially outwardly from turbine blade platforms. The turbine blade platforms and the radially inner and outer bands are also referred to as end walls with regard to the airfoils, particularly in the region of intersection of the airfoils and the bands and platforms.
When the hot gas flow approaches turbine airfoils, there are flow boundary layers along airfoil surfaces and end wall surfaces. At fillets between the airfoils and the end walls, these two boundary layers merge and create a pressure gradient within the boundary layers. This pressure gradient can form a pair of horseshoe vortices at a leading edge of the fillet, one on a pressure side and the other on a suction side of the airfoil. The pressure side vortices travel downstream along the end wall surface. The suction side vortices travel downstream along the suction side airfoil wall and move radially away from the end wall as they are approach a trailing edge of the airfoil. These vortices cause pressure losses and increase surface heating. It is desirable to minimize the strength of the horseshoe vortices for better aerodynamic performance and lower surface heating.